Experimental Physics and
Industrial Control System

From: Johnson, Andrew N. <[email protected]>
Sent: Tuesday, 24 December 2019 11:56 PM
To: STARRITT, Andrew <[email protected]>
Cc: EPICS Tech Talk ([email protected]) <[email protected]>
Subject: Re: subArray record [SEC=UNOFFICIAL]

 

The code change that Michael pointed out was a correction to the original subArray record code – the maximum number of elements of a CA channel should be fixed since many clients rely on that to allocate local storage for channel data, but as you saw unfortunately the subArray code was returning NELM or NORD, both of which can be changed at runtime. cainfo reports the maximum array size, not the current size.

 

However from 3.15.1 onward you may be able to avoid having to use any subArray records at all since the IOC’s CA server supports channel filters, and specifically the array filter. To fetch the item at index 30 you should be able to do this:

 

$ caget 'SR07BM01FPM01:FILL_PATTERN_ABS_WAVEFORM.[30:30]'

 

I believe cainfo with that channel name will also report a single element.

 

HTH,

 

- Andrew

 

 

 

-----Original Message-----
From: Michael Davidsaver <[email protected]>
Sent: Tuesday, 24 December 2019 12:42 PM
To: STARRITT, Andrew <[email protected]>
Cc: EPICS Tech Talk ([email protected]) <[email protected]>
Subject: Re: subArray record [SEC=UNOFFICIAL]

 

On 12/23/19 5:13 PM, STARRITT, Andrew via Tech-talk wrote:

> ...

> My questions: Is this a bug or a feature?

 

https://github.com/epics-base/epics-base/commit/3edc4b5c18741d1c17fd93d63498c2fe2bf594da#diff-3aae14301cf71a07ec8d5a307a827f46L172

 

While I haven't spent much time on subArrayRecord, the current code looks correct.

no_elements should be set to the maximum element count here.  Code which

actually reads from this field should be calling rset::get_array_info() to find

the actual length (from NORD).

 

The previous code wouldn't work properly if the array size ever changed with clients connected.

 

How many elements are are shown by:

 

> camonitor -# 0 SR07BM01FPM01:FILL_PATTERN_ELEMENT_030_EXTRACT